Device for moving a print element carrier in typewriters

ABSTRACT

In a typewriter or similar printing machine the print element carrier is moved by virtue of the cooperation between a lead screw stationarily supported in the machine frame and a rotatable nut member supported in the print element carrier and threadedly engaging the lead screw. The print element carrier supports a clutch which has two inputs including driven components continuously rotated in opposite directions. An escapement mechanism, when in its normal, non-actuated condition, locks both inputs for preventing any driving torque to be transmitted to the nut member by either continuously driven component. A twoposition selector mechanism locks either the one or the other input. When the escapement mechanism is actuated, the latter is withdrawn from both inputs and, as a result, a driving torque is transmitted to the nut member solely by that clutch input which is not locked by the selector mechanism.

United States Patent Behrens et al.

[451 Sept. 17, 1974 DEVICE FOR MOVING A PRINT ELEMENT CARRIER IN TYPEWRITERS [75] Inventors: Herbert Behrens, Neuenburg;

Gunther Wohlbier, Grafschaft, both of Germany [73] Assignee: Olympia Werke A.G.,

Wilhelmshaven, Germany [22] Filed: Aug. 21, 1973 [21] Appl. No.: 390,204

[30] Foreign Application Priority Data Aug. 30, 1972 Germany 2242663 [52] US. Cl. 197/82, 74/441 [51] Int. Cl B41j 19/00 [58] Field of Search 197/82, 84 R, 90, 16, 18, 197/60, 65; 74/441 [56] References Cited UNITED STATES PATENTS 2,498,897 2/1950 Riedel.... 74/441 2,909,935 /1959 Dodge... 197/64 X 3,135,371 6/1964 Young i 197/16 3,225,886 12/1965 Cetran et a1. 197/84 3,313,389 4/1967 Cralle 197/82 Primary Examiner-Robert E. Pulfrey Assistant Examiner-R. T. Rader Attorney, Agent, or FirmSpencer & Kaye [57] ABSTRACT In a typewriter or similar printing machine the print element carrier is moved by virtue of the cooperation between a lead screw stationarily supported in the machine frame and a rotatable nut member supported in the print element carrier and threadedly engaging the lead screw. The print element carrier supports a clutch which has two inputs including driven components continuously rotated in opposite directions. An escapement mechanism, when in its normal, nonactuated condition, locks both inputs for preventing any driving torque to be transmitted to the nut member by either continuously driven component. A twoposition selector mechanism locks either the one or the other input. When the escapement mechanism is actuated, the latter is withdrawn from both inputs and, as a result, a driving torque is transmitted to the nut member solely by that clutch input which is not locked by the selector mechanism.

Claims, 2 Drawing Figures 55 59 T 64 l /l-1r PATENTEDSEPI 71914 SHEET 1 OF 2 mm \\G mv DEVICE FOR MOVING A PRINT ELEMENT CARRIER IN TYPEWRITERS BACKGROUND OF THE INVENTION This invention relates to a device for moving the print element carrier of a typewriter or similar business ma chine and is of the type which has a lead screw supported by the machine frame, a nut member supported in the print element carrier coaxially with the lead screw and an actuatable driving mechanism which, for effecting stepwise or continuous movements of the print element carrier, causes a relative motion between the lead screw and the nut member selectively in one or the other direction of motion.

Carrier moving mechanisms of the afore-outlined type are known such as disclosed, for example, in the U. S. Pat. No. 3,313,389 in which there is provided a lead screw axially rotatably, but longitudinally non-displaceably supported in the machine frame. The lead screw cooperates with a coaxially arranged nut member which is affixed to the print element carrier. The stepwise movement of the carrier in the forward or the reverse direction is controlled by an escapement mechanism which is connected to one end of the lead screw. With the other end of the lead screw there is connected a driving or force-exerting mechanism which comprises a spring motor that moves the carrier in the forward (typing) direction by rotating the lead screw when the print element carrier is freed by the escapement mechanism for performing individual steps or a tabulating operation. Although such an arrangement has been found satisfactory, particularly with respect to a reliable and accurate operation of the escapement mechanism and in connection with the cancellation of forces generated, for example, during the braking of moving masses, it has, with respect to certain functions, significant disadvantages to be discussed hereinafter.

Typewriters of the type that have, for example, a generally spherical print element supported by the carrier, are also used as so-called line printers in data processing machines. In such line printers, in general, much higher operational speeds are required than in regular, correspondence-type typewriters. One of the most important requirements in this respect is to maintain as small as possible those masses which are to be accelerated or braked for either the stepwise movements, or the resetting or tabulating movements of the print element carrier. In prior art devices, as exemplified by the aforementioned United States patent, however, these masses are relatively large, because for each stepwise movement the lead screw has to be accelerated and then arrested. This also applies to the escapement mechanism and the driving mechanism. Further, these lead screws which are at least as long as a print line (which, in bookkeeping machines may have a length of three feet) are likely to undergo torsional oscillations which may result in noise phenomena in the entire machine and may cause an unclear, blurred print. Because of these reasons, print-ing devices having an escapement mechanism of the afore-described type can be driven only with operational speeds which are within the speed range required of correspondence-type typewriters. For a satisfactory operation of line printers, it is generally further required that the greatest possible number of components for the control of all functions of the printing mechanism be disposed in the print element carrier itself to permit a practically universal use of the printing device, since then between a data processing machine and the printing device only electrical energy transmission means, such as a cable or the like has to be additionally provided.

SUMMARY OF THE INVENTION It is an object of the invention to provide a device for moving a print element carrier of the type outlined above which ensures with simple means that the masses to be accelerated and decelerated may be reduced to a minimum, and in which the means for controlling the carrier movements are arranged in the print element carrier itself.

These objects and others to become apparent as the specification progresses, are accomplished by the invention according to which, briefly stated, the print element carrier of the typewriter is moved by virtue of the cooperation between a lead screw stationarily supported in the machine frame and a rotatable nut member supported in the print element carrier and threadedly engaging the lead screw. The print element carrier supports a clutch which has two inputs including driven components continuously rotated in opposite directions. An escapement mechanism, when in its normal, non-actuated condition, locks both inputs for preventing any driving torque to be transmitted to the nut member by either continuously driven component. A two-position selector mechanism locks either the one or the other input. When the escapement mechanism is actuated, the latter is withdrawn from both inputs and, as a result, a driving torque is transmitted to the nut member solely by that clutch input which is not locked by the selector mechanism.

With the device according to the invention it is accomplished that by using a lead screw drive for triggering the carrier movements, only small masses have to be controlled and that practically all components necessary for effecting the carrier movements can be disposed on the carrier itself. An additional substantial advantage resides in the fact that the total number of required components is substantially reduced which is significant regarding economical considerations and the simplicity of the device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional plan view of a preferred embodiment of the invention.

FIG. 2 is a top plan view of a detail of the same embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to FIG. 1, there is illustrated a preferred embodiment of a device for moving a print element carrier 30, which is movably supported on a rail affixed to a frame 31 of a business machine. The rail is constituted by a continuously driven main drive shaft 32. The latter also supplies the input power for other devices (not shown) controlling other functions such as print element carrier setting, margin setting, ink ribbon control and the like.

To the main drive shaft 32 there is connected a driving member 33 which rotates with the shaft 32 as a unit, and, which is, together with the print element carrier 30, linearly displaceable along and with respect to the shaft 32. The driving member 33 is constituted by a gear block having two gear wheels 11 and 12 and forms, with an intermediate pinion 14, a reversing gearing which continuously drives, in opposite directions, two inputs 15 and 16 of a singleand multi-revolution clutch mechanism 13 controllable in both rotary directions. The clutch mechanism 13 which operates as the drive means for the print element carrier is formed of a yoke spring clutch of the type described in detail in German Published Patent Application No. 2,055,101 (published Mar. 16, 1972). The inputs l5 and 16 of the clutch include driven components constituted by input gear wheels 34 and 35 respectively, each provided with a respective, integral clutch sleeve 36 and 37. The input gear wheels 34 and 35 are each connectable to an output shaft 42 by yoke springs 38 and 39. The springs 38 and 39 are, with one of their ends, secured in a respective control sleeve 40 and 41, and, with their other end engage the output shaft 42. The yoke springs 38 and 39 are secured to the output shaft 42 by respective shackles 17 and 18 in an adjustable manner. The yoke spring 38 and the control sleeve 40 form a clutching member which, by virtue of mechanisms described later, is adapted to drivingly connect the input gear wheel 34 to the output shaft 42. Similarly, the yoke spring 39 and the control sleeve 41 form a clutching member which is adapted to cause a transmission of a driving torque from the input gear wheel 35 to the output shaft 42.

The output shaft 42 is provided with an axial throughgoing bore 43 which, in a central zone, has a threaded portion 44 which meshes with a lead screw 45 arranged coaxially with the shaft 42. The threaded portion 44 forms, with a collar-like enlargement of the shaft 42, the nut element of the lead screw-and-nut assembly. The lead screw 45 is supported in the machine frame 31 parallel to the main drive shaft 32. The lead screw 45 has at one end a gear wheel 46 with which it can be immoblized in two, 180 opposed positions by means of a setting member 47 that may be locked in two positions for a purpose which will become apparent later.

The output shaft 42 is rotatably supported in radial and thrust bearings 48 and 49 affixed to the printing element carrier 30. One of the bearings 48, 49 is adjustable to set an axial play. It is thus seen that in the preferred embodiment, the screw-and-nut assembly is formed by the stationary lead screw 45 and by the rotatable nut member constituted by the components 42, 43, 44, 50. It is noted that a lead screw-and-nut assembly, in which the lead screw is stationary and the nut member is arranged for rotation is described, for example in US. Pat. No. 2,498,897, issued Feb. 28, 1950 (inventor: K.A. Riedel).

Also referring now to FIG. 2, in a projection 54 of the collar 50 of the output shaft 42, there is provided an axially extending longitudinal groove 51 in which there is shiftably positioned a selector member or control slide 52. The control slide 52 is provided with a bore into which extends the free leg of a spring 53 which is secured, as illustrated in FIG. 2, to the collar 50 of the output shaft 42. The free leg of the spring 53 projects through a slot 55 provided in the projection 54. The slot 55 serves simultaneously to limit the linear displacement of the control slide 52 and to secure the same in the groove 51.

The control slide 52, dependent upon its axial position, cooperates either with a control lug 56 or a control lug 57 provided on the control sleeves 40 and 41, respectively. The spring 53 biases the control slide 52 continuously in the direction of the control lug 57 of the control sleeve 41. From this position the control slide 52 may be shifted to its other position (where it cooperates with the lug 56) by means of a second triggering pulse emitter formed of a control solenoid II and a control lug 19 attached to the solenoid armature.

In the carrier 30 there is further pivotally supported an escapement bridge 58, which is provided with escapement levers 59 and 60. The latter cooperate with respective actuating members 61 and 62 freely rotatably supported on the escapement bridge 58. The actuating members 61 and 62 are each urged by respective springs 63 and 64 into their operational engagement with the associated respective lugs 56 and 57 of the control sleeves 40 and 41. The actuating members 61 and 62 may be simultaneously swung out of their operative engagement with lugs 56 and 57 against the force of the springs 63 and 64 by means of the escapement bridge 58 which, against the force of a spring 65, is pivotable by an escapement solenoid I. The latter, the escapement bridge 58 and the escapement levers 59 and constitute a first triggering pulse emitter.

For effecting a stepwise advance of the carrier 30 (Le. the release of triggering of individual steps in the typing direction), the escapement solenoid I is briefly energized, whereupon the escapement bridge 58 lifts both actuating members 61 and 62 out of the zone of the control lugs 56 and 57. As a result, the control sleeve 40 is freed, while the control sleeve 41 remains locked by virtue of the control slide 52. Once freed, the control sleeve 40, urged by the yoke spring 38, snaps forwardly and thereby couples the output shaft 42 to the continuously driven clutch component 36. Since the escapement solenoid I is again immediately deenergized, the actuating member 61 and also the actuating member 62 again engage the outer periphery of the associated control sleeves 40 and 41, respectively. As a result, the output shaft 42 is arrested by the control sleeve 40 after one revolution. Since the pitch of the nut member 44 and the lead screw 45 corresponds to the desired step division, for each revolution of the output shaft 42 there is obtained one exact printing step.

If the printing element carrier 30 is to be moved rapidly in the typing direction, that is, it is to perform a continuous motion (for example, a tabulation movement), the escapement solenoid I, subsequent to its energization, remains in the attracted position whereby a continuous run of the yoke spring clutch 13 is achieved by virtue of the driving connection with the left-hand clutch component 36 until the actuating members 61 and 62 are again released by the escapement bridge 58 and are thus allowed to drop in the travelling path of the control lugs 56 and 57.

For effecting a stepwise or a continuous movement of the carrier 30 in a reverse direction (for a reset, a carrier return or a reverse tabulation), the operation is the same as described above, with the difference that above-described release motion of the actuating members 61 and 62 it is now the control sleeve 41 which is freed and the control sleeve 40 is locked. Once freed, the control sleeve 41, urged by the associated yoke spring 39, snaps forwardly and thereby couples the clutch component 37, which rotates continuously in the reverse direction with respect to clutch component 38, to the output shaft 42. As a result, the output shaft 42, its nut member 44, 50 cooperating with the stationary lead screw 45, moves the carrier in a direction opposite to the printing direction. Since the control slide 52 is secured to the output shaft 42, 50, it executes therewith its rotary motions during which the control slide 52 is locked in its position by virtue of the lateral face 66 which forms part of the control lug 57 and which projects into the locking direction. This condition is maintained until the control sleeve 41 is again arrested by the actuating member 62, whereupon the driving connection between the continuously rotating clutch component and the output shaft 42 is interrupted. It will thus be readily understood that for any operation involving the movement of the print element carrier 30 along the line of print (such an operation is initiated, for example, by the depression of a key on the key-board of the typewriter), the energizing circuit for the escapement solenoid is closed. If such movement by the print element carrier 30 is to be effected in a reverse direction (for example, for reset or carrier return), then, in addition to the escapement solenoid I, the energizing circuit for the selector solenoid II is also closed.

When the carrier 30 for effecting typing corrections or for the purpose of margin equalization, should be reset by half a space or should be advanced from such a half-space adjustment in normal, full-space steps, the lead screw 45 is rotated through the gear wheel 46 by the locking member 47 into a 180 opposite position in which it is locked against rotation. Since the pitch of the lead screw 45 is so designed that one relative revolution of the lead screw 45 with respect to the output shaft 42 corresponds to one typing space, such as 180 rotary adjustment of the lead screw 45 results in a halfspace shift of the carrier 30.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

We claim:

1. ln a type printing business machine having a machine frame, a print element carrier arranged for movement along the line of print, a lead screw supported in the machine frame parallel to the line of print, a nut member threadedly engaging the lead screw and supported in the print element carrier, the latter being moved along the line of print upon relative rotation between the lead screw and the nut member, the improvement comprising in combination:

a. means for operationally stationarily supporting said lead screw in said machine frame;

b. first driving means supported in said print element carrier for continuous rotation in a first direction;

0. second driving means supported in said print element carrier for continuous rotation in a second, opposite direction;

d. means for imparting a continuous rotation to said first and second driving means;

e. means for rotatably supporting said nut member in said print element carrier;

f. a clutch supported in said print element carrier and including 1. a first input means having a first position for maintaining said nut member disengaged from said first driving means and a second position for drivingly connecting said first drive means with said nut member to rotate the latter in one direction;

2. a second input means having a first position for maintaining said nut member disengaged from said second driving means and a second position for drivingly connecting said second drive means with said nut member to rotate the latter in an opposite direction;

3. means urging said first and second input means into their respective said first positions;

g. first trigger signal emitting means including 1. escapement means having a first position for simultaneously locking said first and second input means of said clutch in their respective said first positions, said escapement means having a second position in which it is withdrawn simultaneously from said first and second input means;

2. means for actuating said escapement means for moving said escapement means into its said second position;

h. a selector member supported in said print element carrier and having a first position in which it is withdrawn from said first input means and locks said second input means in its first position, said selector member having a second position in which it is withdrawn from said second input means and locks said first input means in its first position; and

i. second trigger signal emitting means connected to said selector member for selectively moving said selector member from one of its said positions into the other.

2. An improvement as defined in claim 1, said nut member including an output shaft having an axial bore, said output shaft being arranged coaxially about said lead screw, said axial bore having a threaded portion threadedly engaging said lead screw; said output shaft having, in the zone of said threaded portion, a collarlike enlargement, said threaded portion and said collarlike enlargement constituting a nut element.

3. An improvement as defined in claim 1, wherein said first trigger signal emitting means is supported in said print element carrier.

4. An improvement as defined in claim 1, wherein said second trigger signal emitting means is supported in said print element carrier.

5. An improvement as defined in claim 1, said means actuating said escapement means including an energizable escapement solenoid; said escapement means including an escapement bridge pivotally supported in said print element carrier, means operatively connecting said escapement solenoid with said escapement bridge, actuating members freely rotatably supported on said escapement bridge and cooperating with said input means of said clutch, spring means urging said actuating members into a locking engagement with said first and second input means, said locking engagement corresponds to said first position of said escapement means, said escapement means further including escapement levers affixed to said escapement bridge and operatively connected to said actuating members for moving the latter against the force of said spring means into a withdrawn position with respect to said first and second input means of said clutch in the energized condition of said escapement solenoid, said withdrawn position corresponds to said second position of said escapement means.

6. An improvement as defined in claim 1, including axially aligned radial and thrust bearings mounted in said print element carrier; said bearings receiving axial ends of said nut member for rotatably supporting the same, one of said bearings being adjustable for setting the axial play of said nut member.

7. An improvement as defined in claim 1, wherein said first and second input means of said clutch respectively include a. first and second clutch input gear wheels connected for continuous, oppositely directed rotation to said first and second driving means, respectively; and

b. first and second clutching members for selectively coupling said first or said second clutch input gear wheel to said nut member for rotating the latter.

8. An improvement as defined in claim 7, further comprising a main drive shaft supported in said machine frame parallel to said lead screw and arranged for guiding said print element carrier; means for continuously rotating said main drive shaft; a gear wheel block secured to said main drive shaft to rotate therewith as a unit, said gear wheel block being arranged on said main drive shaft for linear displacement with respect thereto, said gear wheel block having a first gear wheel constituting said first driving means and meshing with said first clutch input gear wheel, said gear wheel block having a second gear wheel constituting said second driving means and meshing with a reversing pinion, said reversing pinion meshing with said second clutch input gear wheel.

9. An improvement as defined in claim 1, wherein the pitch of the thread of said lead screw and said nut member is of such a magnitude as to cause said print element carrier to axially shift by one typing space upon one revolution of said nut member with respect to said lead screw.

10. An improvement as defined in claim 9, said lead screw having two operative positions 180 apart; further comprising means for rotating said lead screw into, and immobilizing the same in either one of said two operative positions.

11. An improvement as defined in claim 1, including spring means urging said selector member into one of its said two positions; said second trigger signal emitting means includes an energizable control solenoid having an armature connected to said selector member;

said control solenoid, when energized, shifting said selector member into the other of its two said positions against the force of said spring means.

12. An improvement as defined in claim 11, wherein said one of said two input means of said clutch includes means for preventing said selector member from being moved by said spring means from said other of its two positions to said one of its two positions for at least one revolution of said one of said two input means.

13. An improvement as defined in claim 11, said selector member being constituted by a control slide; said nut member including means defining a groove in which said control slide is received and supported for reciprocating motion; said spring means is in engagement with said control slide to urge the latter into a position in which it locks one of said two input means in its said first position. I

14. An improvement as defined in claim 13, wherein said spring means is constituted by a spring member being affixed to said nut member and having a leg portion; said control slide including means defining an opening; said nut member including means defining a slot extending along and immediately adjacent said groove; said'leg portion of said spring member passes through said slot and said opening.

15. In a type printing business machine having a machine frame, a print element carrier arranged for movement along the line of print, a lead screw supported in the machine frame parallel to the line of print, a nut member threadedly engaging the lead screw and supported in the print element carrier, the latter being moved along the line of print upon relative rotation between the lead screw and the nut member, the improvement comprsing in combination:

a. means for operationally stationarily supporting said lead screw in said machine frame;

b. means for rotatably supporting said nut member in said print element carrier;

c. a clutch supported in said print element carrier and having two input means arranged for cooperation with said nut member; each input means having a driven component;

(1. means for continuously rotating said driven components of said two input means in mutually opposite directions;

e. a two-position selector means for selectively maintaining one of said input means locked and the other of said input means simultaneously unlocked;

and

f. escapement means having a deenergized position for maintaining both input means disengaged from said nut member and an energized position for operatively coupling that input means to said nut member which is maintained unlocked by said selector means, whereby a driving torque of preselected sense is applied to said nut member. 

1. In a type printing business machine having a machine frame, a print element carrier arranged for movement along the line of print, a lead screw supported in the machine frame parallel to the line of print, a nut member threadedly engaging the lead screw and supported in the print element carrier, the latter being moved along the line of print upon relative rotation between the lead screw and the nut member, the improvement comprising in combination: a. means for operationally stationarily supporting said lead screw in said machine frame; b. first driving means supported in said print element carrier for continuous rotation in a first direction; c. second driving means supported in said print element carrier for continuous rotation in a second, opposite direction; d. means for imparting a continuous rotation to said first and second driving means; e. means for rotatably supporting said nut member in said print element carrier; f. a clutch supported in said print element carrier and including
 1. a first input means having a first position for maintaining said nut member disengaged from said first driving means and a second position for drivingly connecting said first drive means with said nut member to rotate the latter in one direction;
 2. a second input means having a first position for maintaining said nut member disengaged from said second driving means and a second position for drivingly connecting said second drive means with said nut member to rotate the latter in an opposite direction;
 3. means urging said first and second input means into their respective said first positions; g. first trigger signal emitting means including
 1. escapement means having a first position for simultaneously locking said first and second input means of said clutch in their respective said first positions, said escapement means having a second position in which it is withdrawn simultaneously from said first and second input means;
 2. means for actuating said escapement means for moving said escapement means into its said second position; h. a selector member supported in said print element carrier and having a first position in which it is withdrawn from said first input means and locks said second input means in its first position, said selector member having a second position in which it is withdrawn froM said second input means and locks said first input means in its first position; and i. second trigger signal emitting means connected to said selector member for selectively moving said selector member from one of its said positions into the other.
 2. a second input means having a first position for maintaining said nut member disengaged from said second driving means and a second position for drivingly connecting said second drive means with said nut member to rotate the latter in an opposite direction;
 2. means for actuating said escapement means for moving said escapement means into its said second position; h. a selector member supported in said print element carrier and having a first position in which it is withdrawn from said first input means and locks said second input means in its first position, said selector member having a second position in which it is withdrawn froM said second input means and locks said first input means in its first position; and i. second trigger signal emitting means connected to said selector member for selectively moving said selector member from one of its said positions into the other.
 2. An improvement as defined in claim 1, said nut member including an output shaft having an axial bore, said output shaft being arranged coaxially about said lead screw, said axial bore having a threaded portion threadedly engaging said lead screw; said output shaft having, in the zone of said threaded portion, a collar-like enlargement, said threaded portion and said collar-like enlargement constituting a nut element.
 3. An improvement as defined in claim 1, wherein said first trigger signal emitting means is supported in said print element carrier.
 3. means urging said first and second input means into their respective said first positions; g. first trigger signal emitting means including
 4. An improvement as defined in claim 1, wherein said second trigger signal emitting means is supported in said print element carrier.
 5. An improvement as defined in claim 1, said means actuating said escapement means including an energizable escapement solenoid; said escapement means including an escapement bridge pivotally supported in said print element carrier, means operatively connecting said escapement solenoid with said escapement bridge, actuating members freely rotatably supported on said escapement bridge and cooperating with said input means of said clutch, spring means urging said actuating members into a locking engagement with said first and second input means, said locking engagement corresponds to said first position of said escapement means, said escapement means further including escapement levers affixed to said escapement bridge and operatively connected to said actuating members for moving the latter against the force of said spring means into a withdrawn position with respect to said first and second input means of said clutch in the energized condition of said escapement solenoid, said withdrawn position corresponds to said second position of said escapement means.
 6. An improvement as defined in claim 1, including axially aligned radial and thrust bearings mounted in said print element carrier; said bearings receiving axial ends of said nut member for rotatably supporting the same, one of said bearings being adjustable for setting the axial play of said nut member.
 7. An improvement as defined in claim 1, wherein said first and second input means of said clutch respectively include a. first and second clutch input gear wheels connected for continuous, oppositely directed rotation to said first and second driving means, respectively; and b. first and second clutching members for selectively coupling said first or said second clutch input gear wheel to said nut member for rotating the latter.
 8. An improvement as defined in claim 7, further comprising a main drive shaft supported in said machine frame parallel to said lead screw and arranged for guiding said print element carrier; means for continuously rotating said main drive shaft; a gear wheel block secured to said main drive shaft to rotate therewith as a unit, said gear wheel block being arranged on said main drive shaft for linear displacement with respect thereto, said gear wheel block having a first gear wheel constituting said first driving means and meshing with said first clutch input gear wheel, said gear wheel block having a second gear wheel constituting said second driving means and meshing with a reversing pinion, said reversing pinion meshing with said second clutch input gear wheel.
 9. An improvement as defined in claim 1, wherein the pitch of the thread of said lead screw and said nut member is of such a magnitude as to cause said print element carrier to axially shift by one typing space upon one revolution of said nut member with respect to said lead screw.
 10. An improvement as defined in claim 9, said lead screw having two operative positions 180* apart; further comprising means for rotating said lead screw into, and immobilizing the same in either one of said two operative positions.
 11. An improvement as defined in claim 1, including spring means urging said selector member into one of its said two positions; said second trigger signal emitting means includes an energizable control solenoid having an armature connected to said selector member; said control solenoid, when energized, shifting said selector member into the other of its two said positions against the force of said spring means.
 12. An improvement as defined in claim 11, wherein said one of said two input means of said clutch includes means for preventing said selector member from being moved by said spring means from said other of its two positions to said one of its two positions for at least one revolution of said one of said two input means.
 13. An improvement as defined in claim 11, said selector member being constituted by a control slide; said nut member including means defining a groove in which said control slide is received and supported for reciprocating motion; said spring means is in engagement with said control slide to urge the latter into a position in which it locks one of said two input means in its said first position.
 14. An improvement as defined in claim 13, wherein said spring means is constituted by a spring member being affixed to said nut member and having a leg portion; said control slide including means defining an opening; said nut member including means defining a slot extending along and immediately adjacent said groove; said leg portion of said spring member passes through said slot and said opening.
 15. In a type printing business machine having a machine frame, a print element carrier arranged for movement along the line of print, a lead screw supported in the machine frame parallel to the line of print, a nut member threadedly engaging the lead screw and supported in the print element carrier, the latter being moved along the line of print upon relative rotation between the lead screw and the nut member, the improvement comprsing in combination: a. means for operationally stationarily supporting said lead screw in said machine frame; b. means for rotatably supporting said nut member in said print element carrier; c. a clutch supported in said print element carrier and having two input means arranged for cooperation with said nut member; each input means having a driven component; d. means for continuously rotating said driven components of said two input means in mutually opposite directions; e. a two-position selector means for selectively maintaining one of said input means locked and the other of said input means simultaneously unlocked; and f. escapement means having a deenergized position for maintaining both input means disengaged from said nut member and an energized position for operatively coupling that input means to said nut member which is maintained unlocked by said selector means, whereby a driving torque of preselected sense is applied to said nut member. 